It's the highest level, people argue that football is more tactical now but things were more vigorous back then and tactics came about because of men like Pele, Maradona inspiring others, tbh I'd only put Cruijf from the non winners among them as he impacted football's approach. You're basically facing the best of each nation.
Many players have talent but comparing players solely on that is flawed as even similar talents have different approaches to them hence why influence of a team is looked at and the hardest stage to do it is at major tournaments, talent wise the are players technically better than even the legends and even greats like Messi and Ronaldo but their control of their ability is not there. The same goes with stats as people will claim numbers don't lie sure but they sure can misinterpret the truth, Messi has more goals for Argentina than any other player but how many of those came in the thrashing of minnows at some tournaments before going on to be knock out by teams who knew how to defend.
People also knock the current team Argentina has and say that's what holds Messi back yet Brazil and Argentina back when Pele and Maradona played were written off, the 1970's Brazilian team were thought to have no hope in hell as they previously went out in the group stages in 1966, it's funny how looking at it retrospectively changes views. I remember Argentina 2006 had a good team.
Club level is all nice and good but playing for Barcelona is obviously going to help you find a winners medal considering the status of the club and the era under such logic it would be like comparing Rooney to Bobby Charlton, the former has won more at club level but at international level has had nowhere near the same influence. The are big differences to playing at club level and international from financial power, more games on a home turf, team mates more geared to how you play, opponents you know a lot better, environment you're used to (weather etc...), longer campaign for success yes but than you have more time to recover from any slump and more chances to win etc... Best way I can put it even though it'll sound harsh is the's a differences with someone doing well playing Street Fighter on Xbox Live than at Evo, yeah the will also be some strong opponents in the former but it has more leeway and is closer to your comfort zone unlike the the latter.
Not winning a major tournament doesn't mean Messi is far worse than these players as he'll still go down as a great player but if you want to be compared to legends you need to at least achieve something on the highest level like they did.